7. Antonine Plague
Death toll: 5 million
Year: 165–180 AD
In 165 AD, Roman legions were laying siege to Seleucia. While there, they contracted a mysterious disease that was quick to spread throughout garrisons in Roman Empire. The illness was merciless, and about 25 percent of those who contracted it died. It ravaged throughout Rome, killing about 5 million people in the empire. During its height, some 2,000 people perished daily in Rome itself. The Greek physician Galen left a thorough account of the epidemics and modern scientists assume, based on his descriptions of the symptoms, that the disease in question was smallpox.
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